Re: [PATCH 5/5] KVM: selftests: add shared hugetlbfs backing source type

[Ben Gardon]

On Wed, May 12, 2021 at 2:45 PM Axel Rasmussen <axelrasmussen@xxxxxxxxxx> wrote:
>
> This lets us run the demand paging test on top of a shared
> hugetlbfs-backed area. The "shared" is key, as this allows us to
> exercise userfaultfd minor faults on hugetlbfs.
>
> Signed-off-by: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
> ---
>  tools/testing/selftests/kvm/demand_paging_test.c |  6 ++++--
>  tools/testing/selftests/kvm/include/test_util.h  | 10 ++++++++++
>  tools/testing/selftests/kvm/lib/kvm_util.c       |  9 +++++++--
>  tools/testing/selftests/kvm/lib/test_util.c      |  6 ++++++
>  4 files changed, 27 insertions(+), 4 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/demand_paging_test.c b/tools/testing/selftests/kvm/demand_paging_test.c
> index ff29aaea3120..32942c9e0376 100644
> --- a/tools/testing/selftests/kvm/demand_paging_test.c
> +++ b/tools/testing/selftests/kvm/demand_paging_test.c
> @@ -502,8 +502,10 @@ int main(int argc, char *argv[])
>                 }
>         }
>
> -       TEST_ASSERT(p.uffd_mode != UFFDIO_REGISTER_MODE_MINOR || p.src_type == VM_MEM_SRC_SHMEM,
> -                   "userfaultfd MINOR mode requires shared memory; pick a different -t");
> +       if (p.uffd_mode == UFFDIO_REGISTER_MODE_MINOR &&
> +           !backing_src_is_shared(p.src_type)) {
> +               TEST_FAIL("userfaultfd MINOR mode requires shared memory; pick a different -t");
> +       }
>
>         for_each_guest_mode(run_test, &p);
>
> diff --git a/tools/testing/selftests/kvm/include/test_util.h b/tools/testing/selftests/kvm/include/test_util.h
> index 7377f00469ef..852d6d2cc285 100644
> --- a/tools/testing/selftests/kvm/include/test_util.h
> +++ b/tools/testing/selftests/kvm/include/test_util.h
> @@ -85,9 +85,19 @@ enum vm_mem_backing_src_type {
>         VM_MEM_SRC_ANONYMOUS_HUGETLB_2GB,
>         VM_MEM_SRC_ANONYMOUS_HUGETLB_16GB,
>         VM_MEM_SRC_SHMEM,
> +       VM_MEM_SRC_SHARED_HUGETLB,
>         NUM_SRC_TYPES,
>  };
>
> +/*
> + * Whether or not the given source type is shared memory (as opposed to
> + * anonymous).
> + */
> +static inline bool backing_src_is_shared(enum vm_mem_backing_src_type t)
> +{
> +       return t == VM_MEM_SRC_SHMEM || t == VM_MEM_SRC_SHARED_HUGETLB;
> +}

Would it make sense to check (vm_mem_backing_src_alias(t)->flag &
MAP_SHARED) == MAP_SHARED instead?

> +
>  struct vm_mem_backing_src_alias {
>         const char *name;
>         uint32_t flag;
> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> index 838d58633f7e..fed02153c919 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> @@ -756,8 +756,13 @@ void vm_userspace_mem_region_add(struct kvm_vm *vm,
>                 region->mmap_size += alignment;
>
>         region->fd = -1;
> -       if (src_type == VM_MEM_SRC_SHMEM) {
> -               region->fd = memfd_create("kvm_selftest", MFD_CLOEXEC);
> +       if (backing_src_is_shared(src_type)) {
> +               int memfd_flags = MFD_CLOEXEC;
> +
> +               if (src_type == VM_MEM_SRC_SHARED_HUGETLB)
> +                       memfd_flags |= MFD_HUGETLB;
> +
> +               region->fd = memfd_create("kvm_selftest", memfd_flags);
>                 TEST_ASSERT(region->fd != -1,
>                             "memfd_create failed, errno: %i", errno);
>
> diff --git a/tools/testing/selftests/kvm/lib/test_util.c b/tools/testing/selftests/kvm/lib/test_util.c
> index c7a265da5090..65fb8b43782c 100644
> --- a/tools/testing/selftests/kvm/lib/test_util.c
> +++ b/tools/testing/selftests/kvm/lib/test_util.c
> @@ -240,6 +240,11 @@ const struct vm_mem_backing_src_alias *vm_mem_backing_src_alias(uint32_t i)
>                         .name = "shmem",
>                         .flag = MAP_SHARED,
>                 },
> +               [VM_MEM_SRC_SHARED_HUGETLB] = {
> +                       .name = "shared_hugetlb",
> +                       /* No MAP_HUGETLB, we use MFD_HUGETLB instead. */

Is it worth calling out the difference between the two flags here?

> +                       .flag = MAP_SHARED,
> +               },
>         };
>         _Static_assert(ARRAY_SIZE(aliases) == NUM_SRC_TYPES,
>                        "Missing new backing src types?");
> @@ -262,6 +267,7 @@ size_t get_backing_src_pagesz(uint32_t i)
>         case VM_MEM_SRC_ANONYMOUS_THP:
>                 return get_trans_hugepagesz();
>         case VM_MEM_SRC_ANONYMOUS_HUGETLB:
> +       case VM_MEM_SRC_SHARED_HUGETLB:
>                 return get_def_hugetlb_pagesz();
>         default:
>                 return MAP_HUGE_PAGE_SIZE(flag);
> --
> 2.31.1.607.g51e8a6a459-goog
>